B cell disorders, also termed as humoral deficiency states, may involve all or selective antibody classes, either due to abnormal B cell disorders differentiation (quantitative) or inability to respond against a specific antigen (qualitative). Many cases are secondary to T-cell defects.
Clinically, these cases present with variable severity of recurrent sinopulmonary infections or bacteremia, usually due to encapsulated organisms e.g. S. pneumoniae, H.influenzae and Staph. nureus.
Typically, B cell disorders do not manifest in first 3 months of life due to presence of transplacental antibodies from mother.
Diagnosis is usually established by measured nonspecific immunoglobulin levels or specific antibody titers, after vaccination e.g. DPT.
Management of these cases includes
a) IVIG therapy (400-500 mg/kg/months) and
b) prophylactic antibiotics.
Some important and common B cell disorders are as follows —
Transient hypogammaglobulinemia indicates developmental delay in Immunoglobulin production during early infancy, due to delayed maturation ofT- helper cells.
This leads to accentuated physiological nadir in Ig levels at 3-5 months (<200 mg/dl), with spontaneous recovery by 18-24 months.
Bruton (X-linked) agammaglobulinemia, seen only in males, is a maturation defect from pre-B-cell stage to mature B-cell stage, characterized by severe hypogammaglobulinemia and absence/hypoplasia of lymphoid tissue, manifesting in late infancy or early childhood.
Common variable immunodeficiency disorder (CVID) is a maturation defect from mature B-cell stage to plasma cell differentiation, characterized by late onset after 1St decade, normal/enlarged lymphoid tissue frequently associated with splenomegaly, autoimmune disorders e.g. thrombocytopeni c purpura or hemolytic anemia, and malignancies.
Selective IgA deficiency is commonest (1:600) but rarely symptomatic B cell disorders, characterized by low serum IgA levels (<5-10 mg/dl). Symptomatic cases present with recurrent sino-pulmonary infections, food allergy and autoimmune/rheumatologic disorders.
Hyper 1gM Syndrome is characterized by inability to produce antigen-specific antibody response despite elevated 1gM and normal tgG/IgA levels, due to a genetic I-cell defect in activating B-cell response causing B cell disorders.
Apart from 5mb-pulmonary infections, Hematologic autoimmune disorders or intracellular infections e.g. TB are common.
B cells or B – Lymphocytes are mediators of acquired humoral immunity, by production of antigen-specific or non-specific immunoglobulins.
Like T-cells, these cells also develop from stem-cells in bone marrow in the human body.
However, unlike them, human B cells mature in bone marrow itself (Bursa of fabricus in birds), before circulating and populating lymphoid follicles in spleen, liver, tonsils and Peyer’s patches. They comprise 5-15% of total circulating lymphocytes.
On antigenic stimulus, these cells differentiate into plasma cells, to produce various immunoglobulins.
B cells are of two types – B1 (CD5) cells, which produce non-specific 1gM immunoglobulins against variety of antigens; and those which produce specific 1gM, IgE and IgA antibodies in response to specific antigenic challenge.
